The present invention relates to an apparatus for use in processing food products where it is desired to maintain the products in compression during processing. More particularly, the invention relates to a meat processing apparatus, especially adaptable for processing hams, in which the products are held compressed between pairs of vertically adjustable shelves during the cooking or curing process.
A wide variety of devices useful for processing food products, such as hams, which are most desirably compressed during processing are known in the art. Such devices are also adapted for high volume production and, therefore, are constructed to accommodate a fairly large number of products, but in a fairly compact arrangement. It is also desirable to maintain the products in a spaced relationship, both horizontally and vertically, so that the products are uniformly and completely exposed to the processing atmosphere. The processing may, for example, comprise cooking, smoking, or other curing process.
One common prior art construction is the so-called "ham press" in which a box-like framework contains a series of vertically spaced product carrying shelves, above each of which is located a vertically adjustable compression shelf which can be moved downwardly to bear upon the hams or other products lying on product shelves and hole them in compression during processing. The shelves are most often porous plates or screens which are rigid enough to transmit the desired compressive force, but which will also provide ready access of the processing atmosphere to the food products.
The typical prior art ham press also includes means for conveying or moving it into and out of a processing chamber. One common arrangement is to simply provide the device with supporting wheels or, in an alternate construction, the device may utilize overhead rollers to adapt the press for movement along a monorail or similar conveying system.
Various arrangements for providing relative movement between the product shelves and the compression shelves in a ham press are shown in the art, as are means for varying the level of compressive force to which the hams or other products may be subjected. In U.S. Pat. No. 3,618,511 the compression shelves are biased to move toward the product shelves by the force of vertically disposed compression springs. The springs are first compressed, as through the use of an air cylinder, to force the shelves apart for loading the hams to be cooked or cured on the product shelves. Release of the force of the air cylinder after loading, causes the compression springs to force the upper compression shelves down against the hams and to compress the same therebetween. The patent also discloses the use of spacer members between opposing shelves to limit the final process spacing. However, since the force exerted by a compressed coil spring will very substantially, depending upon its state of compression (or, conversely, extension), the actual compressive load exerted by this device will depend largely upon the size of the hams or other products being processed and, indeed, the utility of this device may be rather severely restricted to a rather narrow range of product sizes.
Another prior art ham press utilizes the dead weight of the product shelves as well as the products thereon to exert a compressive force on the products contained on lower level shelves. These compressive forces may be supplemented by the active compressive force of a coil spring arrangement. However, because of the cumulative increase in dead load from top to bottom, there is a lack of uniformity of compression from one shelf to another. U.S. Pat. No. 4,341,154 discloses an individual spring-loaded compression device for each set of trays wherein the supplemental force may be decreased from top to bottom of the stack of shelf pairs, so that the combined pressure resulting from the dead weight and the auxiliary compression will be more uniform. The construction, however, is quite complex and requires individual adjustment of each of auxiliary compression means for each shelf pair.
U.S. Pat. No. 4,658,718 also discloses the use of compression springs to press a unitary assembly of compression shelves against an interposed assembly of product shelves. The length of the compression springs is adjustable to vary the amount of compressive force exerted. However, no provision is made for shelf to shelf dead weight compensation.
Thus, the prior art is characterized by devices which utilize dead weight compression and/or spring-loaded compression which, in many prior art devices, may vary considerably from shelf to shelf in a vertical direction. In addition, it is difficult to control initial product size as the products are loaded onto the press and, as a result, both initial and final compression, as well as final product size, may vary from shelf to shelf and also on the same shelf.